Diversity and abundance of arthropod floral visitor and herbivore assemblages on exotic and native Senecio species
Eve M. WhiteA,B, John C. WilsonA and Anthony R. ClarkeA
A School of Natural Resource Sciences, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia.
B Current address: Alan Fletcher Research Station, Department of Natural Resources and Water and CRC for Australian Weed Management, PO Box 36, Sherwood, Queensland 4075, Australia.
The enemy release hypothesis predicts that native herbivores prefer native, rather than exotic plants, giving invaders a competitive advantage. In contrast, the biotic resistance hypothesis states that many invaders are prevented from establishing because of competitive interactions, including herbivory, with native fauna and flora. Success or failure of spread and establishment might also be influenced by the presence or absence of mutualists, such as pollinators. Senecio madagascariensis (fireweed), an annual weed from South Africa, inhabits a similar range in Australia to the related native S. pinnatifolius. The aim of this study was to determine, within the context of invasion biology theory, whether the two Senecio species share insect fauna, including floral visitors and herbivores. Surveys were carried out in south-east Queensland on allopatric populations of the two Senecio species, with collected insects identified to morphospecies. Floral visitor assemblages were variable between populations. However, the two Senecio species shared the two most abundant floral visitors, honeybees and hoverflies. Herbivore assemblages, comprising mainly hemipterans of the families Cicadellidae and Miridae, were variable between sites and no patterns could be detected between Senecio species at the morphospecies level. However, when insect assemblages were pooled (i.e. community level analysis), S. pinnatifolius was shown to host a greater total abundance and richness of herbivores. Senecio madagascariensis is unlikely to be constrained by lack of pollinators in its new range and may benefit from lower levels of herbivory compared to its native congener S. pinnatifolius.
Key words: Biotic resistance, fireweed, floral visitors, herbivory, invasive species, natural enemies, pollination,species richness.
Plant Protection Quarterly (2008) 23 (2) 90-98.